Wednesday, April 24, 2013

Maybe no mathematical double of the universe

Peter Woit trashes a new book by physicist Lee Smolin, and quotes Smolin saying:

The most radical suggestion arising from this direction of thought is the insistence on the reality of the present moment and, beyond that, the principle that all that is real is so in the present moment. To the extent that this is a fruitful idea, physics can no longer be understood as the search for a precisely identical mathematical double of the universe. That dream must be seen now as a metaphysical fantasy that may have inspired generations of theorists but is now blocking the path to further progress. Mathematics will continue to be a handmaiden to science, but she can no longer be the Queen.

I doubt that I will agree with Smolin's main claims, but I do agree that it is a mistake to believe that physics should be a precisely identical mathematical double of the universe. My FQXi essay explains why.

But it was much worse than that when I realized that the author was leading up to a type of "hidden variables" interpretation of Quantum Mechanics (QM). If you don't know what that term means, don't worry about it, it is just physics jargon for theories that try to replace QM by deterministic approaches that avoid the probabilistic interpretation of it. Based on personal philosophy and even religion, countless people (many of them very prominent physicists themselves) objected to the standard probabilistic interpretation of QM in the last 90 years. Hundreds of alternative deterministic approaches were proposed to replace QM. These theories are termed "hidden variable theories." The better ones actually reproduce most of the predictions of QM. But no hidden variable theory has ever produced identical results to QM for all test cases. When the differences arose in predictions, the experiments backed the predictions by QM irrefutably. As of today, there is not one single hidden variable theory that produces the same results as QM for all experiments. It may yet happen some day, but based on how hard some of the smartest people on Earth have tried and failed for 90 years (including most notably Albert Einstein) to make hidden variable theories work, the prospects are rather dim.

As if that was not bad enough, in the last few chapters the author rejects the concept of "identical particles" in QM.

I haven't seen the book, but pursuit of hidden variable theories is severely misguided, as I have argued here, and criticized Smolin here.

Lubos Motl calls the book An incredible pile of unscientific gibberish. Motl also trashes Aaronson's book here and here, and if you just read those posts, you would get the impression that Motl has a very low opinion of Aaronson. See also the comments, which did not display in my preferred browsers. No, those posts are only mild criticisms compared to the venom for Smolin.

Aaronson is really a smart theoretical computer scientist with a warped view of physics. I am sure that his book is mostly correct, even if it is over-enthusiastic about some ideas. But Smolin subscribes to a philosophy that is antagonistic to modern science. Smolin once gave this definition of science:

Science is not about what's true, or what might be true. Science is about what people with originally diverse viewpoints can be forced to believe by the weight of public evidence.